Well biofouling is a complex and yet not sufficiently understood process. Water wells represent a unique habitat, since they create a link between the anaerobic ground water, containing Fe(II) and the aerobic surface. These special conditions set ideal conditions for the growth of iron bacteria (Stuetz and McLaughlan, 2004). Some of these bacteria are known to be responsible for well clogging by precipitation of iron hydroxides (Cullimore, 1999). The consistency of the ochres can range from soft and bulky to solid and compact. The type of deposit strongly depends on the dominant species of bacteria at the well screen and inside the gravel pack. Within this project (WellMa) a sampling system was created, which allowed the collection of unaffected biofilm samples from inside the wells. The samples were microscopically examined, DNA was extracted and community profiles were created.